My recollection of sickle mowers is from about 50 years ago. It worked great for cutting alfalfa, which was what we used exclusively for hay back then on the dairy farm. Also good for clipping pastures, my least favorite job during the dog days of summer. But it had a hard time cutting through thick grass, and sharpening/replacing sections was a never-ending chore. The inherent offset is definitely a plus.
Edit: I definitely would not have attempted cutting 1" diameter brush with the one we had, but perhaps there are modern ones that can do it.